1. Technical Field
The present invention relates to a solid-state imaging device with a stacked photoelectric conversion film and an imaging apparatus including the solid-state imaging device.
2. Related Art
In conventional, commonly used CCD and CMOS image sensors (solid-state imaging devices), a photodetecting region (effective pixel region) consisting of plural pixels (photoelectric conversion portions, photodiodes) that are arranged in two-dimensional array form is formed in a semiconductor substrate surface portion and subject image signals corresponding to a subject optical image formed on the photodetecting region are output from the respective pixels. An optical black (OB) region that is covered with a light shield film is formed around the photodetecting region, and an offset component of each of subject image signals that are output from the photodetecting region is removed using, as a reference signal, a dark signal that is output from the OB region.
Subtracting a noise component (dark current; equal to an output of the OB region) that thermally occurs even without incident light from each subject image signal (each output of the photodetecting region) makes it possible to detect, with high accuracy, faint subject image signals that are output from the photodetecting region and to thereby realize a solid-state imaging device having a large S/N ratio.
In the above-described conventional CCD and CMOS solid-state imaging devices, the photoelectric conversion portions (photodiodes) and signal reading circuits (charge transfer channels and an output amplifier in the case of the CCD type and MOS transistor circuits in the case of the CMOS type) need to be formed in the same semiconductor substrate surface portion. This raises a state that the ratio of the total area of the photoelectric conversion portions to the chip area of the solid-state imaging device cannot be set to 100%. A recent trend of a decreasing aperture ratio due to miniaturization of pixels is a factor of S/N ratio reduction.
In these circumstances, attention has come to be paid to solid-state imaging devices that are configured in such a manner that photoelectric conversion portions are not formed on a semiconductor substrate and only signal reading circuits are formed on the semiconductor substrate and that a photoelectric conversion film is formed above the semiconductor substrate.
For example, in the stack-type solid-state imaging device disclosed in JP-A-6-310699, X rays or electron beams are detected through photoelectric conversion by an amorphous silicon layer, for example, stacked over a semiconductor substrate surface. In the photoelectric conversion film stack-type solid-state imaging device disclosed in JP-A-2006-228938, a color image of a subject is taken by means of three photoelectric conversion layers having a red detection photoelectric conversion film, a green detection photoelectric conversion film, and a blue detection photoelectric conversion film, respectively.
In the solid-state imaging device of JP-A-6-310699, dark current is detected by stacking a 2-μm-thick light shield layer as the topmost layer of the solid-state imaging device around an effective pixel region (photodetecting region). In the solid-state imaging device of JP-A-2006-228938, incidence of light on signal reading circuits is merely prevented by stacking a light shield film between the semiconductor substrate surface and the photoelectric conversion film (bottommost layer). No consideration is given to the structure of an OB region.
In the stack-type solid-state imaging device of JP-A-6-310699, since the 2-μm-thick light shield layer is formed in the OB region, a step of 2 μm is formed between the OB region and the photodetecting region. Diffuse reflection of light incident on the step portion may degrade a subject image. The photoelectric conversion film stack-type solid-state imaging device of JP-A-2006-228938 cannot produce subject image signals having large S/N ratios because dark current cannot be detected in a state that no light is incident on the photoelectric conversion film (i.e., the photoelectric conversion film is shielded from light).